1. Field of the Invention
This invention relates generally to battery systems, and more particularly to regulating pre-charge current in a battery system.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Examples of portable information handling systems include notebook computers. These portable electronic devices are typically powered by battery systems such as lithium ion (“Li-ion”) or nickel metal hydride (“NiMH”) battery packs including one or more rechargeable batteries. FIG. 1 shows a battery system 120 of a portable information handling system 100 having battery charge terminals 122, 124 that are temporarily coupled to corresponding charge output terminals 115, 116 of a battery charging apparatus 110. As so configured, battery charging apparatus 110 is coupled to receive current from current supply terminals 112, 114 (e.g., alternating current, or direct current from an AC adapter) and to provide DC charging current to battery charge terminals 122, 124 of battery system 120 via charge output terminals 115, 116. As shown, battery system 120 also includes battery system data bus terminals 126, 128 for providing battery state information, such as battery voltage, to corresponding battery charging apparatus data bus terminals 117, 118.
FIG. 2 shows a conventional lithium ion battery system 120 having a battery management unit (“BMU”) 202 responsible for monitoring battery system operation and for controlling battery system charge and discharge circuitry 270 that is present to charge and discharge one or more battery cells of the battery system. As shown, BMU 202 includes analog front end (“AFE”) 206 and microcontroller 204. Charge and discharge circuitry 270 of battery system 120 includes two field effect transistors (“FETs”) 214 and 216 coupled in series between battery charge terminal 122 and battery cell/s 224. FET 214 is a charge FET switching element that forms a part of charge circuit 260 that is controlled by the microcontroller 204 and/or AFE 206 of BMU 202 using switch 218 to allow or disallow charging current to the lithium ion battery cell/s 224, and FET 216 is a discharge FET switching element that forms a part of discharge circuit 262 that is controlled by microcontroller 204 and/or AFE 206 of BMU 202 using switch 220 to allow or disallow discharge current from the battery cell/s 224. As shown, parasitic diodes are present across the source and drain of each FET switching element, i.e., to conduct charging current to the battery cell/s when the discharge FET switching element 216 is open, and to conduct discharging current from the battery cell/s when the charge FET switching element 214 is open.
During normal battery pack operations both charge and discharge FET switching elements 214 and 216 are placed in the closed state by respective switches 218 and 220, and cell voltage detect circuitry 210 of AFE 206 monitors voltage of battery cell/s 224. If cell voltage detect circuitry 210 of AFE 206 detects a battery over-voltage condition, BMU 202 opens the charge FET switching element 214 to prevent further charging of the battery cell/s until the over-voltage condition is no longer present. Similarly, if the cell voltage detect circuitry 210 of AFE 206 detects a battery under-voltage (or over-discharge) condition, BMU 202 opens the discharge FET switching element 216 to prevent further discharging of the battery cell/s until the under-voltage condition is no longer present. BMU 202 may also open the charge FET switching element 214 when the battery pack is in sleep mode. A current sense resistor 212 is present in the battery pack circuitry to allow current sensor 208 of AFE 206 to monitor charging current to the battery cell/s. If the charge FET switching element 214 is supposed to be open (e.g., during sleep mode or battery over-voltage condition) but charging current is detected, BMU 202 permanently disables the battery pack by blowing an inline fuse 222 present in the battery circuitry to open the battery pack circuitry and prevent further over-charging.
When Li-ion and NiMH battery cells have been discharged to a certain low voltage level, they are not ready to receive their full charging current and must be “pre-charged” at a much lower current level. For example, a typical minimum charging current from a smart charger is 128 milliamperes, which may be sufficiently low for pre-charging some NiMH battery cells. However, the required pre-charge current for other types of battery cells may be much lower than 128 milliamperes. For a typical Li-ion battery cell, the required pre-charge current is about 20 milliamperes or less per cell. To provide the required pre-charge current, separate pre-charge circuitry has been incorporated into a battery pack to achieve the desired pre-charge current level by reducing the charging current supplied by a battery charging apparatus.
FIG. 2 illustrates pre-charge circuitry 250 that is present in charge and discharge circuitry 270 to pre-charge battery cell/s 224 when battery cell/s 224 have been discharged to a predetermined low voltage level and are not ready to receive their full charging current. As shown, pre-charge circuitry 250 includes MOSFET 252, used as a switch, and a resistor 254 to limit the level of the pre-charge current to a much lower current value than the charging current provided by battery charging apparatus 110. During pre-charging mode, microcontroller 204 turns on MOSFET switch 252 when cell voltage detect circuitry 210 of AFE 206 detects that voltage of battery cell/s 224 is below the predetermined low voltage level and the pre-charge current level is needed. During pre-charge mode, BMU 202 also maintains charge FET switching element 214 in open state to limit the charging current provided to battery cell/s 224 to the lower pre-charge current level. When voltage of battery cell/s 224 reaches the predetermined low voltage level, BMU 202 turns off MOSFET 252 and closes charge FET switching element 214 to allow the full charging current to be provided to battery cell/s 224.
As shown in FIG. 2, pre-charge circuitry 250 of conventional lithium ion battery system 120 requires provision of separate circuitry components in the battery system. Due to safety and cost reasons, no such pre-charge circuitry components may be provided for some battery systems, such as NiMH battery systems. In such systems, components of the battery charging apparatus are used to regulate the pre-charge current level.